An electronic device may include one or more circuit card modules inserted into a chassis and electronically coupled to a backplane of the electronic device. A typical circuit card module includes one or more circuit boards mounted to a heat sink structure. A typical circuit board is a planar board that mechanically supports electronic components. The electronic components may comprise, for example, resistors, capacitors, switches, batteries, and other more complex integrated circuit components, i.e. microprocessors. The circuit board typically comprises a dielectric material, for example, a plastic material.
A simple circuit board may include conductive traces on its surface for connecting the electronic components to each other. As electronic circuitry has become more complex, multi-layer circuit boards with at least two electrically conductive trace layers sandwiched between dielectric layers have been developed. Typically, the different conductive trace layers of the multi-layer circuit board may be connected through vertically extending vias, which comprise conductive materials, for example, metal.
A typical backplane includes conductive traces sandwiched between dielectric layers similar to the circuit board construction. The backplane may allow two or more circuit card modules to interconnect through electrically conductive pads on the major surfaces thereof. In other words, the edge surface of the circuit card module is mounted onto the major surface of the backplane at a 90 degree angle. Moreover, this interconnection is typically accomplished using an interconnector component on the major surface of the circuit card module and the backplane. Typically, the interconnector component physically couples the circuit card module and backplane together and electrically couples the electrically conductive pads.
As circuit card modules become more densely populated with heat generating components, such as processors, multi-chip modules (MCMs), radio frequency (RF), photonic devices and field-programmable gate arrays (FPGAs), the dissipation of the heat generated has become increasingly more important. One heat dissipation approach, which has been used in a variety of applications, including electronic circuit card modules, has been to use convection cooling techniques. With convection cooling, the circuit card modules may be mounted in the electronic device in a way that permits cooling air to flow over the circuit boards. For proper convection cooling, an adequate cooling airflow over a sufficiently exposed surface of the circuit board should be provided. Such arrangements may be incompatible, however, with some uses of circuit card modules where cooling air is not available or space is not available to allow adequate airflow over heat dissipating components.
An alternative approach is to dissipate heat through conduction. In this application, heat is transferred via a heat sink positioned on one surface of the circuit board and in contact with components on the circuit board. The heat sink includes a flange extending beyond the sides of the circuit board allowing for attachment to the cold wall of the electronic device chassis. Typically wedge lock retainer devices are used to make the connection between the heat sink flanges and the electronic device chassis. This conduction approach is the basis of industry standards such as VITA 48.2 and IEEE 1101.2. Advancements in heat management technology, such as heat sinks embedded with pyrolytic graphite and heat pipes, have been used to address increasing heat dissipation demands. However, the thermal resistance created by the wedge lock retainer devices make them a less efficient method and a limiting factor in conducting high heat loads away from circuit boards.